Browsing by Author "Ji, S"

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    High‐voltage‐driven surface structuring and electrochemical stabilization of Ni‐rich layered cathode materials for Li rechargeable batteries
    (Wiley, 2020-05-04) Song, SH; Cho, M; Park, I; Yoo, JG; Ko, KT; Hong, J; Kim, J; Jung, SK; Avdeev, M; Ji, S; Lee, S; Bang, J; Kim, H
    Layered lithium–nickel–cobalt–manganese oxide (NCM) materials have emerged as promising alternative cathode materials owing to their high energy density and electrochemical stability. Although high reversible capacity has been achieved for Ni‐rich NCM materials when charged beyond 4.2 V versus Li+/Li, full lithium utilization is hindered by the pronounced structural degradation and electrolyte decomposition. Herein, the unexpected realization of sustained working voltage as well as improved electrochemical performance upon electrochemical cycling at a high operating voltage of 4.9 V in the Ni‐rich NCM LiNi0.895Co0.085Mn0.02O2 is presented. The improved electrochemical performance at a high working voltage at 4.9 V is attributed to the removal of the resistive Ni2+O rock‐salt surface layer, which stabilizes the voltage profile and improves retention of the energy density during electrochemical cycling. The manifestation of the layered Ni2+O rock‐salt phase along with the structural evolution related to the metal dissolution are probed using in situ X‐ray diffraction, neutron diffraction, transmission electron microscopy, and X‐ray absorption spectroscopy. The findings help unravel the structural complexities associated with high working voltages and offer insight for the design of advanced battery materials, enabling the realization of fully reversible lithium extraction in Ni‐rich NCM materials. © 2020 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim
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    Magnetic-field-induced instability of the cooperative paramagnetic state in ZnxCo(4-x)(OD)6Cl2
    (American Physcical Society, 2012-05-29) Dissanayake, SE; Chan, C; Ji, S; Lee, J; Qiu, Y; Rule, KC; Lake, B; Green, MA; Hagihala, M; Zheng, XG; Ng, TK; Lee, SH
    Using elastic and inelastic neutron scattering techniques with and without application of an external magnetic field H, the magnetic ground states of ZnxCo(4-x)(OD)6Cl2 (x = 0,1) were studied. Our results show that for x = 0, the ground state is a magnetic long-range ordered (LRO) state where each tetrahedron forms an "umbrella"-type structure. On the other hand, for x = 1, no static ordering was observed down to 1.5 K, which resembles the behavior found in the isostructural quantum system ZnxCo(4-x)(OD)6Cl2. When H field is applied, however, the x = 1 system develops the same LRO state as x = 0. This indicates that the x = 1 disordered state is in the vicinity of the x = 0 ordered state. © 2012, American Physical Society.